Lex felt the overwhelming power of annihilation, and began to appreciate how genuinely awesome the power of laws could be. He knew that he could not genuinely be hurt during this challenge of the tower, probably, but even then, the power of annihilation felt like it would devour him. More importantly, if the application of the law didn't allow for a challenger to directly overcome the effects of the law, Lex knew this would have been the end of his climb in the tower.
Yet the clear loophole was there, and so Lex survived some version of the attack that destroyed a whole realm. He was certain that it was not really on the same scale as the realm destroying attack, but it was impressive nonetheless. It would have been even more impressive if he knew exactly which one of the many things inhabiting his body allowed him to do it.